The invention relates generally to self-aligned bipolar transistors. More particularly, the invention relates to self-aligned emitter-base transistors having a selectively grown silicon link between the intrinsic and extrinsic bases.
Bipolar transistors having, for example, a silicon germanium (SiGe) intrinsic base and a polysilicon extrinsic base are frequently used in integrated circuits fabricated for high performance mixed signal applications. In bipolar transistors (BTs) and high performance heterojunction bipolar transistors (HBTs), it is desirable to have relatively small size, high cutoff frequency (Ft) and maximum oscillation frequency (Fmax). Fmax is a function of Ft and of parasitics, including parasitic capacitances and parasitic resistances. Exemplary parasitics include but are not limited to: collector-base capacitance Ccb, base-emitter Cbe capacitance, and base resistance Rb. It has been a challenge, however, to fabricate very small transistors that operate in, for example, the 90 nanometer (nm) technology node, which are capable of accurately amplifying electrical signals at a frequency of about 300 GHz, and of being integrated with 90 nm CMOS devices as well as other passives and other features.